The US Department of Energy estimates that alternating current motors consume more than 65% of the electricity produced today and total electricity sales in the US will increase at an average annual rate of 1.9%, from 3,481 billion kilowatt hours in 2001 to 5,220 billion kilowatt hours in 2025. With a reduction in electrical energy consumption by 33%, by today's measure, is equivalent to the total output of 840 fossil fuel-based power plants. Throughout the world, electricity is used at an average rate of 40 billion kilowatt-hours each day, with a projected average annual growth rate of 2.3% for the next 20 years.
With few exceptions, much of the electricity is not used in the form in which it was initially produced. Rather, it is reprocessed to provide the type of power needed in the technology that is being employed. Power electronics convert electrical power from one form to another. By the end of this decade, it is expected that up to 80% of electrical power will be processed by power electronics equipment and systems.
To control a brushless direct current (BLDC) motor, it is critical to know the rotor position. One known method is to fit Hall Effect Sensors inside the motor to detect the rotor position. This method has the disadvantage of fitting the hall sensors (including components and assembly costs). Sensorless control methods do not have this disadvantage. There are at least two different types of sensorless control methods: 1) detecting the back-emf zero crossing; and 2) space vector control (or field oriented control).
The back-emf zero crossing detecting method is more suitable for motors with trapezoidal back-emf. The noise margin at zero crossing for this type of motor is relatively large since the zero crossing is sharp as shown in FIG. 4.
But for BLAC (Sinusoidal back-emf) motor, the zero crossing is more gradual, therefore noise margin at zero crossing is much smaller as shown in FIG. 5. The space vector control method on the other hand is ideally suited for BLDC with sinusoidal back emf. It consists of controlling the components of the motor stator currents, represented by a vector, in a rotating reference frame d,q aligned with the rotor flux. It requires the dynamic model equations of the motor and returns the instantaneous currents and voltages in order to calculate and control the variables. So-called Clarke and Park transformation will take place to translate the stator variables (currents and angle) into a flux model. This flux model is compared with the reference values and updated by a PI controller. After a back transformation from field to stator coordinates, the output voltage will be impressed to the machine with Pulse Width Modulation (PWM).